The interlayer inserted between active layer and ITO has been a key issue for improving electron extraction in inverted polymer solar cells (IPSCs), while the ideal interlayer for IPSCs has not been well developed. In this work, we presented a spontaneous vertical phase separation (SVPS) self-assembled bilayers structure with BenMelm-CI ionic liquid (IL) interfacial bottom layer and a photoactive top layer via a single spin-coated step of BenMelm-CI IL and organic donor-acceptor composite and achieved a PCE as high as 8% based on IPSCs with PTB7 as the donor. The presence of BenMelm-CI IL reduces the work function of ITO and leads to a better energy-level matching for efficient charge-transfer. The driving force of SVPS selfassembled structure is from the relative surface energy difference between organic materials and BenMelm-CI ILs, together with their interactions with the substrates. This self-assembled process procedure pave the way to simplify the manufacturing of low-cost and large-area organic electronic devices. (C) 2015 Elsevier Ltd. All rights reserved.